The invention relates to a linear drive comprising a housing having a tube body containing a receiving space for a linearly moving drive part and a housing cover mounted on an end side of the tube body, a peripherally closed cavity formed in the wall of the tube body, which cavity is open toward the tube body""s end face facing the housing cover, and at least one socket, which is provided as an axial extension of the cavity on the housing cover and also provided for the rear end section of a sensor serving for detection of at least one position of the drive part, said sensor extending from the socket into the cavity in the tube body.
A linear drive of this type is described in the German patent publication 4,306,539 C2. In this known case the tube body possesses a channel-like cavity, formed the wall thereof and aligned with a socket, in the form of a receiving hole, in the housing cover mounted at the end. The sensor is designed in the form of rod and is plugged from the rear side of the housing cover through the receiving hole into the cavity in the tube body, the rear end section of the sensor being fixed in the receiving hole. At the rear end section of the sensor electrical leads are provided and associated with the rear side (opposite to the tube body) of the housing cover whence same make possible electrical contact and connection with the sensor.
In the case of linear drive the measure necessary for the holding in place of the sensor on the housing cover take up a relatively large space in the longitudinal direction of the linear drive. Same accordingly has a relatively large overall length. Therefore it is one object of the present invention to create a linear drive, which while providing for secure holding of the sensor in place has a small overall length.
In order to achieve this object there is a provision such that the socket is constituted by a recess in the housing cover, the opening of such recess extending from the end face, facing the tube body, of the housing cover continuously as far as the adjacent lateral outer face of the housing cover, the electrical lead means of the sensor being associated with the lateral section of the recess""s opening.
It is in this manner that the rear end section of the sensor is seated in a recess, extending along a corner of the housing cover, the electrical contact with the sensor being possible from the side of the housing cover. The length, as measured in the longitudinal direction of the linear drive of the recess may be made relative short, something which means short dimensions of the housing cover and provides space within the housing cover for other means, which are necessary for the operation of the linear drive. Since the electrical lead means of the sensor are associated with the lateral section of the recess""s opening, satisfactory accessibility is provided for. Finally it is also possible to ensure unloseable fixation of the sensor in place, since deinstillation is only possible by removal of the housing cover, this preventing unauthorized access.
Further advantageous developments of the invention are defined in the dependent claims.
It is preferred for the rear end section of the sensor to be in the form of an attachment section, by way of which the sensor is so held in the recess, that, as considered in the state with the tube body removed, it extends firmly held in a transverse position, that is to say it is secured in the transverse direction and practically incapable of movement, extending away from the housing cover. Therefore when mounting the sensor in place it is possible to firstly secure same with the attachment section in the recess in the housing cover in order in the course of later fixing of the housing cover on the tube body to simultaneously insert outwardly extending longitudinal section of the sensor into the cavity.
It is particularly advantageous for the rear end section of the sensor to be designed in the form of an attachment section, which renders possible plugged mounting of the sensor in the recess. In this case a design of the plug connecting means is preferred such that the direction of plugging coincides with the longitudinal direction of the linear drive.
The plug connecting means may for example be constituted by wells, which extend in the direction of plugging on the housing cover, such recesses being provided in the lateral faces of the recess and by lateral projections, fitting in the wells, of the sensor. Furthermore a reversed association of the plug connecting means would be possible here.
A design is preferred such that the sensor has its one attachment section held immovably in the axial direction between the housing cover and the tube body. It is in this manner that an exact, axially secured positioning of the sensor in relation to the housing of the linear drive is ensured without additional attachment means. This is for instance made possible by having the attachment section and the recess so matched in their dimensions that the sensor is proud of the tube body to a small extent when housing cover is not mounted on the tube body so that in the mounted state of the housing cover the tube body is acted upon by the facing end side of the tube body.
It is convenient for the recess to be closed, apart from the opening thereof extending from the end face as far as the lateral external face.
Preferably no fixation of the sensor""s longitudinal section, extending into the cavity in the tube body, is required so that consequently the sensor is conveniently free right from the housing cover along its full length where it projects into the cavity of the tube body and apart from its rear end section is not fixed anywhere. At this point it is to be noted as well that the axial overall length of the sensor""s longitudinal section extending into the cavity is preferably selected to be less than the overall length of the tube body, it being sufficient for the sensor to extend so far into the cavity that the part is covered or the point is reached, which is to be detected.
Preferably the cavity extends along the full overall length of the tube body and opens at the opposite end faces of the tube body. If housing covers are provided on both ends of the tube body and such housing covers have a recess with an associated sensor, it is accordingly possible for both sensors to extend from opposite sides into one and the same cavity.
Since the sensor may readily be so designed that the section of its length extending into the cavity does not require any transverse supporting action, the cross sectional shape of the cavity does not have to meet any special requirements and practically any design is possible. This means that the cross sectional shape of the cavity may be adapted to comply with other features of the tube body. It is for instance possible to have a tube body in the form of a extrude, which in its wall has a plurality of axially continuous channels distributed about the periphery of the receiving space, such channels being provide to save weight and material, one of such channels being utilized as a cavity to receive the sensor.
It is preferred for the electrical lead means of the sensor to be designed in the form of plug means so that a cable may be replaced as desired. Furthermore the sensor preferably has an essentially L-like shape, the longer limb extending into the cavity of the tube body while the shorter limb is provided on the rear end section and extends through the laterally aligned section of the recess""s opening to the outside. In this case the electrical lead means are preferably provided on the shorter L limb of the sensor.
The sensor may be provided with light producing display means on the rear end section, such display means making it possible to indicate the operational state of the sensor. In this connection in the case of a particularly economic structure there may be such a provision that the sensor has a housing which is transparent at least at the rear end section, through which housing the light signals from the light display means are visible from the outside. Accordingly the light producing display means may be readily seen while the display area protected in an optimum manner.
The design in accordance with the invention is more particularly advantageous in the case of linear drives operated using fluid power. However, the invention is also applicable to linear drivess, which are operated with other types of energy, as for example electric power.
In the following the invention will be described with reference to the accompanying drawings.